1. Field of Invention
The present invention relates to connection of fiber reinforced structures, in particular the provision of exposed non-resin infused fiber at edges or surfaces of fiber reinforced components, which fiber may be beneficially used to reinforce subsequently formed joints between or to such fiber reinforced components.
2. Description of Related Art
Most adhesively bonded joints in fiber reinforced composites lack any continuity of reinforcement, with the notable exception of Z-pin technology such as is disclosed in U.S. Pat. No. 6,821,368 B2 to Benson et al. Continuity of fiber reinforcement across joints is desirable because the fiber reinforcement is far stronger than the polymer matrix and is stronger yet compared to adhesively bonded joints within a polymer matrix. Polymer joints lacking fiber reinforcement can be expected to lack the inherent fatigue resistance of fiber reinforced structures. Additionally, adhesively bonded joints between polymer structures are subject to environmental degradation. Cured resin systems of composite components leave relatively few sites for chemical bonding to occur when the article is later joined in a secondary bonding step. These limitations of conventional adhesively bonded joints in fiber reinforced composites have been well documented by    J. M. Koyler, et al, Intl. SAMPE Tech. Conf. Series, 45, 365 (2000).    D. M. Gleich, et al, Intl. SAMPE Tech. Conf. Series, 45, 818 (2000).    R. H. Bossi, R. L. Nereberg, Intl. SAMPE Tech. Conf. Series, 45, 1787 (2000).    Heselhurst R. B., Joining Composite Structures, Tutorial notes SAMPE 2001.The above mentioned references are hereby incorporated by reference. U.S. Pat. No. 5,464,059 to Jacaruso et al discloses partial embedment of reinforcing fabric in thermoplastic materials for subsequent connection of thermoset composite structures, but without fiber continuity through the completed thermoset/thermoplastic/thermoset joints suggested therein. The various processes for increasing the surface energy and availability of potential bond sites are labor intensive, expensive, of dubious reliability, and are subject to reversal by brief environmental exposure.
The benefits of z-axis fibers within individual composite articles are known. For example, individual plies of pre-preg material have been treated with flocked fibers in order to obtain improved inter-laminar strength. Three dimensional woven pre-forms have also been used. An example of such 3 dimensional woven pre-forms is disclosed in U.S. Pat. No. 6,712,099 B2 to Schmidt et al. Although such structures may provide superior Z axis delamination resistance within integrally cured components, such structures do not in themselves provide for increased adhesive joint strength. Several methods for providing reinforcement across joints have been proposed in the past. These include U.S. Pat. Nos. 5,879,492 and 6,645,610 B1 to Reis and Wong which disclose the use of peel ply sheets which, when peeled from the cured composite, are intended to leave embedded in the composite structure, fibers which are intended to reinforce a subsequent adhesive joint. The use of both co-woven and flocked fibers is disclosed. Such systems result in the conflicting requirements for good wetting properties of the fibers to be left behind in the cured resin, and for good release properties of the fiber to be peeled away. Obviously, this would not work well with a single type of fiber with a single type of surface treatment. Furthermore, release agents that might be applied to the fibers to be peeled may be prone to migrate during cure onto the fibers to be embedded, thus diminishing the strength and reliability of any adhesive joint which such embedded fibers are intended to reinforce.
Electro-statically flocked carbon fibers have also been used for the purpose of enhancing heat transfer from electrical components and for heat transfer in Stirling engines.